(1) Field of the Invention
The present invention relates to a metal vessel having a circumferential side seam. More particularly, the invention relates to a vessel of a tin-plated steel sheet, which has improved adhesion and corrosion resistance in its circumferential side seam.
(2) Description of the Prior Art
A so-called draw-ironed can is widely used as a vessel for a content having a spontaneous pressure, such as beer or carbonated drink.
This draw-ironed can is prepared by draw-forming a metal blank punched into a disc or the like between a drawing punch and a drawing die into a cup and ironing the side wall of the cup between an ironing punch and an ironing die to reduce the thickness of the side wall.
In the draw-ironed can, in order to reduce the weight of the can per unit volume and lower the cost of the metal blank necessary for the production of the can, it is greatly desired to reduce the thickness of the side wall as much as possible.
However, this desired is greatly limited in the production of cans, and the desire has not been satisfied. More specifically, when the thickness of the side wall of the can body is reduced, the buckling strength will naturally be reduced according to the reduction of the thickness of the side wall. At the step of double-seaming a lid to the can body, the axial load applied to the can body in a seamer is in the range of 120 to 200 Kg, and if the thickness of the side wall portion is reduced below a certain limit, double seaming of a lid to the can body becomes difficult.
The structurally weakest portion in a draw-ironed can is that portion of double seaming between the lid and can body, and breakage or leakage is caused in this portion under a shock given on falling or the like.
A metal bottle formed by lap-bonding open ends of cup-shaped upper and lower members is advantageous in that even if the thickness of the material constituting the seam is extremely small, the bottle can resist a shock of up to the shear strength of the seam irrespective of the thickness of the material and since double seaming is not necessary, the thickness of the side wall of the vessel can be reduced without a fear of buckling.
However, when the circumferential open ends of these upper and lower members are lap-bonded, it is difficult to provide a bonded circumferential seam cpable of resisting a high shear force and excelling in the creep resistance.
In case of straight lap bonding of a can body, both the ends of the formed seam are mechanically fixed by double seaming with can lids, but in case of the above-mentioned circumferential side seam, the entire circumference of the seam is not mechanically fixed at all and the size of the seam is readily changed. Moreover, since the diameter of the open ends are going to change according to the change of the temperature, a stress is readily generated in the adhesive layer. Furthermore, in many cases, the thickness of the open ends to be formed into a seam is reduced, and the formed seam is readily changed by an external force. For the foregoing reasons, it is a problem how to form bondings having a high resistance to a shearing force between the metal blank and the primer coating and between the coating and the adhesive layer.
Among steel blanks, tinplate, that is, a tin-plated steel sheet, has an excellent formability capable of resisting drawing, deep drawing, draw-ironing and the like. However, this blank is insufficient in the adhesion to the coating, and in case of a metal vessel having the above-mentioned circumferential side seam, even if an adhesive having excellent bonding characteristics is used, peeling is readily caused between the tin-plated steel sheet and the coating of an adhesive primer, resulting in such defects as leakage, insufficient sealing, corrosion of the metal blank and dissolution of the metal component into the vessel contents.